High-performance dual-energy imaging with a flat-panel detector: imaging physics from blackboard to benchtop to bedside

Abstract

The application of high-performance flat-panel detectors (FPDs) to dual-energy (DE) imaging offers the potential for dramatically improved detection and characterization of subtle lesions through reduction of "anatomical noise," with applications ranging from thoracic imaging to image-guided interventions. In this work, we investigate DE imaging performance from first principles of image science to preclinical implementation, including: 1.) generalized task-based formulation of NEQ and detectability as a guide to system optimization; 2.) measurements of imaging performance on a DE imaging benchtop; and 3.) a preclinical system developed in our laboratory for cardiac-gated DE chest imaging in a research cohort of 160 patients. Theoretical and benchtop studies directly guide clinical implementation, including the advantages of double-shot versus single-shot DE imaging, the value of differential added filtration between low-and high-kVp projections, and optimal selection of kVp pairs, filtration, and dose allocation. Evaluation of task-based NEQ indicates that the detectability of subtle lung nodules in double-shot DE imaging can exceed that of single-shot DE imaging by a factor of 4 or greater. Filter materials are investigated that not only harden the high-kVp beam (e.g., Cu or Ag) but also soften the low-kVp beam (e.g., Ce or Gd), leading to significantly increased contrast in DE images. A preclinical imaging system suitable for human studies has been constructed based upon insights gained from these theoretical and experimental studies. An important component of the system is a simple and robust means of cardiacgated DE image acquisition, implemented here using a fingertip pulse oximeter. Timing schemes that provide cardiacgated image acquisition on the same or successive heartbeats is described. Preclinical DE images to be acquired under research protocol will afford valuable testing of optimal deployment, facilitate the development of DE CAD, and support comparison of DE diagnostic imaging performance to low-dose CT and radiography.

Optimal kVp selection for dual‐energy imaging of the chest: Evaluation by task‐specific observer preference tests

“…Also, the study was performed such that technique factors other than kVp were fixed. Selection of these factors was based upon previous theoretical and experi- mental studies [7][8][9][10][11] which indicate that they are appropriate ͑even optimal͒ choices-e.g., total filtration of ͑2.5 mm Al͒ in the low-kVp projection, ͑4.5 mm Al+ 0.6 mm Ag͒ in the high-kVp projection, and dose allocation of ϳ0.28. Furthermore, the experiment considered only a single patient thickness ͑24 cm, corresponding approximately to that of an average adult͒.…”

“…The current work was motivated in part by previous theoretical and experimental studies [7][8][9][10][11] involving the extension of cascaded systems analysis to DE imaging and the experimental measurement of DE imaging performance in terms of contrast, noise, and contrast-to-noise ratio ͑CNR͒ as well as NEQ. For the typical imaging conditions considered in the current work ͑e.g., an adult chest of average thickness imaged at total dose equivalent to that of a conventional DR͒, theoretical and experimental results demonstrated a strong dependence of imaging performance on the low-kVp setting ͑significantly increased for lower low kVp͒, a weaker dependence on the high-kVp setting ͑slightly higher for lower high kVp͒, and overall maximization at ͓60/ 120͔ kVp.…”

Diagnostic Performance of a Prototype Dual-Energy Chest Imaging System

“…The system was modified for the purposes of DE imaging to include: 1) a flat-panel detector (Trixell Pixium-4600, Moirans, France) with a ~250 mg/cm 2 CsI:Tl scintillator and 143 µm pixel pitch, 2) a fingertip pulse oximeter to trigger x-ray exposure during diastole for reduction of cardiac motion artifacts, (44) and 3) a multi-position filter wheel within the collimator to change the added filtration between the low-kVp (2.5 mm Al) and high-kVp (2 mm Al + 0.6 mm Ag) exposures, as guided by previous studies of DE image quality performed in our laboratory. (44)(45)(46) The X-ray tube produces a polychromatic beam with spectrum of beam energies distributed around the pre set target tube potential. Therefore, a high-energy filter was selected to "harden" the high energy beam, to reduce spectral overlap between the low-and high-energy projections.…”

“…This was the subject of considerable investigation in our laboratory (45,46,47). Differential filtration between low-and high-kVp projections was selected and an extensive analysis of contrast, Noise Equivalent Quanta (NEQ) and nodule detectability for low-and high -kVp added filtration was performed.…”

Multiscale deformable registration for dual‐energy x‐ray imaging

“…As described in previous work, 27,28 an experimental prototype DE imaging system was developed based upon a Kodak RVG-5100 digital radiography chest stand ͑Carestream Health Inc., Rochester, NY͒. Modifications include: ͑1͒ a high-performance flat-panel detector ͑FPD͒ ͑3000ϫ 3000 pixels, 0.143 mm pixel pitch, CsI:Tl scintillator, Trixel Pixium-4600, Moirans, France͒; ͑2͒ a computercontrolled filter wheel for differential filter selection in lowand high-kVp projections; ͑3͒ a cardiac-gated image acquisition system; and ͑4͒ an acquisition workstation that controls imaging technique, filter selection, and synchronization of the source and FPD.…”